There are essentially two types of dyeing for keratin fibers, for example human keratin fibers such as the hair.
The first, known as oxidation dyeing or permanent dyeing, comprises using oxidation dye precursors, which are colorless or sparingly colored compounds. When they are placed in contact with an oxidizing agent, these compounds produce, via a process of oxidative condensation taking place within the fiber itself, colored substances that remain trapped in the fibers.
The second, known as direct dyeing or semi-permanent dyeing, is obtained by using colored and coloring compounds that have affinity for the keratin fibers onto which they are applied. This type of dyeing does not require the use of an oxidizing agent to reveal the color, although it is not excluded for this type of agent to be present during the process. The latter case is then referred to as lightening direct dyeing.
The dye compositions of the prior art are, in the majority of cases, in the form of liquids, gels or creams, which are mixed, if necessary, before being applied to fibers, with an oxidizing composition.
Dye compositions are usually relatively rich in starting materials, among which are usually found fatty substances, surfactants and/or polymers. These compositions are typically formulated such that they have spreading properties and textures that are easy to work in order to allow quick and easy application to fibers, while at the same time being thick enough not to run beyond the areas that it is desired to color. Furthermore, these compositions should ideally remain stable during the leave-on time on the fibers and should ideally be easy to remove by rinsing once the coloration has been obtained.
It is not uncommon to find that large amounts of starting materials penalize the dyeing qualities of such compositions. Less favorable kinetics, a reduced intensity of the shade obtained, poorer homogeneity of the color from one fiber to another and/or depending on the location of the fiber (root/end), etc. may thus be observed.